We address active sensation in the context of the tactile localization of objects, with an ultimate goal to decode how a perception is converted into a motor act. Our approach is to map the transformation of sensory input within the closed loops of the vibrissa sensorimotor system, in which animals sweep long hairs or vibrissae rhythmically through the space that surrounds their head,. The focus of the proposed new experiments are to delineate the control of brainstem nuclei, both sensory nuclei that transform input sensations and motor nuclei that direct the sensors, by descending cortical projections. Such control is of general relevance to all mammalian sensorimotor systems. The nested, closed loop structure of the rodent vibrissa system is a model for sensorimotor control in mammals up through primates. As a focus for scientific investigation and progress in both computational and health related issues, the vibrissa system enjoys a significant data base of anatomical and electrophysiological data, is compatible with standard molecular and physiological tools, and is amenable to a studies with awake behaving animals, albeit with a reduced behavioral repertoire compared to primates. The proposed experiments involve the cortical activation of brainstem nuclei electrical and optical based physiological and anatomical studies with awake, trained rodents. We begin at the sensory end. 1) Does feedback from primary sensory cortex to brainstem nuclei alter the sensory response? Centrifugal fibers from sensory cortex project to integrative sensory neurons in the brainstem. We will determine if and how this feedback path modulates the gain of the reafferent signal of sensor motion, a basic aspect of proprioception. This may be used, based on our past work, to code touch in terms of coordinates that are normalized to the region of interest. More generally, this work addresses gain of function through high-level control. We next consider an essential missing module in the vibrissa sensorimotor circuit: Where are the brainstem nuclei that drive rhythmic whisking? We ask: 2) Does the rhythm pattern generator of breathing control whisking as well? We ask if the rhythmic generator for breathing acts as a central clock, or if breathing and whisking have independent rhythmic generators that phase-lock under different conditions. This query bears on the general coordination of orofacial behaviors. We then build on this effort and ask: 3) Does feedback from motor cortex control the region of interest of rhythmic whisking? The interpretation of touch in neural pathways depends on how the region of interest that shape vibrissa movements are regulated. We will determine how the slowly varying signals observed in motor cortex are used to guide the range of motion set by brainstem motor nuclei. This query bears on the general issue of coordinating motor output on multiple time-scales. Our data may lead to fundamental concepts in signaling and circuitry in the normal state as well as dysfunction states.